Open Portal GX-9's range

It's fairly simple. Take a party member with you. Place a teleporter down at any position on the map. If you can see your party member on the mini-map, you can place the teleporter there. It gets weird at some maps. For example, at White Fangs (right before Sharp Cliffs), you can place a teleporter on the top platform of mobs and the bottom platform. However, you can only teleport upward. When standing on the top platform, the bottom is out of rendering distance and you cannot teleport down (not a problem because of jump-down). Otherwise, I'd assume the range could be near infinite. It all depends on if both ends are rendered when you stand on one side.